Hypothalamic-Pituitary Axis and Hormones

Overview

• The video discusses the hypothalamic-pituitary axis, focusing on the hypothalamus and pituitary gland.
• Hypothalamus: Located below the thalamus, a master regulator of the endocrine system.
• Pituitary Gland: Sometimes referred to as the hypothesis with two lobes:
  • Anterior Lobe (Adenohypophysis)
  • Posterior Lobe (Neurohypophysis)
• Infundibulum: The stalk connecting the hypothalamus to the pituitary gland.

Communication Mechanisms

• Posterior Pituitary (Neurohypophysis):
  • Hypothalamus has neurons projecting directly to it.
  • Releases hormones produced in the hypothalamus directly into the bloodstream.
• Anterior Pituitary (Adenohypophysis):
  • Hypothalamus communicates through the median eminence and the hypothalamic portal system.
  • Releases hormones into the blood supply, stimulating the anterior pituitary to release its own hormones.

Hormones Released by the Posterior Pituitary

• Antidiuretic Hormone (ADH):
  • Opposes diuretic action, tells kidneys to reabsorb water.
  • Released in times of dehydration to prevent water loss.
• Oxytocin:
  • Stimulates smooth muscle contraction in the uterus and mammary glands.
  • Plays roles in labor (positive feedback mechanism) and milk ejection.
  • Known as the 'love hormone' for its roles in social bonding.

Hormones Released by the Anterior Pituitary

Hypothalamic Hormones that Stimulate Anterior Pituitary

1. Gonadotropin-Releasing Hormone (GnRH):
   • Stimulates release of LH and FSH from anterior pituitary.
2. Growth Hormone-Releasing Hormone (GHRH):
   • Stimulates release of growth hormone.
3. Corticotropin-Releasing Hormone (CRH):
   • Stimulates release of adrenocorticotropic hormone (ACTH).
4. Thyrotropin-Releasing Hormone (TRH):
   • Stimulates release of thyroid-stimulating hormone (TSH).

Anterior Pituitary Hormones

• Lutenizing Hormone (LH) & Follicle Stimulating Hormone (FSH):
  • Stimulate ovaries and testes, playing roles in ovulation, follicle development, and sperm production.
• Growth Hormone (GH):
  • Stimulates growth and protein synthesis in various tissues.
• Adrenocorticotropic Hormone (ACTH):
  • Stimulates adrenal cortex to release cortisol, aldosterone, and androgens.
• Thyroid-Stimulating Hormone (TSH):
  • Stimulates thyroid gland to release thyroid hormones (T3 and T4).

Inhibitory Hormones

• Growth Hormone Inhibitory Hormone (Somatostatin):
  • Inhibits release of growth hormone.
• Prolactin Inhibitory Factor (Dopamine):
  • Inhibits release of prolactin, stopped by suckling action in lactation.

Functions of Hormones

• Cortisol: Regulates glucose metabolism and is released during stress.
• Aldosterone: Increases sodium reabsorption, affecting blood volume.
• Thyroid Hormones: Regulate metabolism, affecting weight and temperature.
• Prolactin: Promotes milk production in mammary glands.

Summary

• The hypothalamic-pituitary axis is crucial for endocrine regulation, involving complex hormone interactions and feedback mechanisms.
• Understanding this axis helps comprehend how the body maintains homeostasis through hormone regulation.